Lightweight Insulating Sandwich-Structured Composite Film for Superior Antireflective EMI Shielding and Infrared...

Developing efficient electromagnetic interference (EMI) shielding materials that are electrically insulating and reflection-suppressed remains a fundamental challenge. Here, we report a lightweight and flexible bacterial cellulose/intercalated NbSe₂/bacterial cellulose sandwich-structured composite film that decouples electromagnetic attenuation from electrical conductivity. Electrochemical intercalation endows few-layer NbSe₂ with expanded interlayer spacing and an accordion-like architecture, enabling strong electromagnetic absorption via multiple internal reflections. Bacterial cellulose provides an insulating surface and suppresses surface reflection via impedance matching, allowing more electromagnetic waves (EMWs) to be absorbed in NbSe₂. The sandwich film with a density of ∼4 g/cm³ and thickness of ∼60 μm achieves broadband EMI shielding efficiency, exceeding 35 dB across 8.2-40.0 GHz while maintaining a reflection of less than 10 dB and ultralow electrical conductivity of ∼10^-3 S·m^-1, effectively preventing electromagnetic pollution and electrical short circuits. The robust cellulose framework imparts excellent flexibility and environmental stability. Moreover, the layered architecture enables effective blocking of wireless charging signals and pronounced infrared camouflage. This work establishes a general structural design strategy for safe, flexible and multifunctional electromagnetic management and infrared camouflage materials.